Rodenticidal baits typically include a carrier and a rodenticide. The rodenticide is the active ingredient and the carrier is often referred to as an inert ingredient. In most rodenticidal baits, the carrier is really not chemically inert, in that it typically contains one or more grains or other foods which are attractive to rodents. The carrier does not, however, typically contribute to the rodenticidal activity of the bait, and thus is inert in that respect.
U.S. Pat. No. 4,815,923 for SWEET CORN BASED RODENTICIDE to Raymon W. Lush issued Mar. 28, 1989 and discloses a rodenticidal bait which includes an active ingredient mixed with an inert ingredient comprising dried sweet corn as a substantial portion thereof. The '923 patent recites that the optimal particle size of the ground corn for such use with Norway and roof rats is between 0.5 mm and 1.5 mm in diameter. In addition, the '923 patent contemplates using ground sweet corn of this grind to form rodenticidal pellets of approximately 3/16 inch in diameter. Experience has shown that such pellets have an average bulk density of less than 45 lbs/ft.sup.3. Rodenticidal efficacy tests disclosed in the '923 patent indicated that when test rats were presented with such pellets and with a challenge bait containing 65% yellow dent corn, 25% rolled oats, 5% corn oil and 5% white sugar but no active ingredient, the pellets containing an active ingredient constituted over one half of the rats' diet and resulted in a 100% mortality rate.
However, unlike test settings where rats, mice or other rodents are maintained in cages or other controlled environments, rodent control is often required in and around barns, silos and other outbuildings which are subject to varying weather conditions. Under such conditions, rodenticidal baits which are not weather resistant are likely to disintegrate and/or turn moldy, with the bait becoming less attractive to rodents and the active ingredient susceptible to leaching and dissolution into water flowing into the surrounding area. Long term rodent control under such conditions necessarily requires frequent bait replacement.
One conventional pellet manufacturing technique for sweet-corn rodenticidal pellets utilizes a pelletizing mill 8 like that schematically shown in FIG. 1. The mill 8 includes a drum 10 having a pelleting cavity 12 in which are positioned rollers 14. Formed in drum 10 and extending from the inside wall 16 of drum 10 to the outside wall 18 thereof are a plurality of radial die holes 20, with one or more knives 22 positioned adjacent outside wall 18. To produce rodenticidal pellets, material 24 to be pelleted is fed continuously into pelleting cavity 12 while drum 10 is rotated. Rotation of drum 10 causes rollers 14 to turn in the same direction, with two wedges 26 of material 24 formed thereby. Material 24 is compressed by the wedging action of drum 10 and rollers 14, forced through die holes 20, and sheared by knives 22 to form rodenticidal pellets 28.
While the pelletizing technique described above does involve the application of pressure to form rodenticidal pellets, the density of such pellets is typically sufficient only to prevent excessive pellet attrition and dust formation during pellet packaging, shipping and distribution. Pellet density is typically not consistent enough to overcome a tendency of the pellets to disintegrate in a wet environment. It appears that lack of precise control over the length of time the material to be pelleted stays in the die holes may contribute to variable pellet density.
Weather resistant rodenticidal baits are available. However, many conventional weather resistant baits include wax to provide a weather resistant quality. Incorporating wax can be problematic for at least two reasons. First, elevated temperatures required for wax liquefaction can be detrimental to some rodenticides due for certain active ingredients which degrade at elevated temperatures. Second, even with rodenticides which are stable at elevated temperatures, rodenticidal baits containing wax are typically less attractive to the target rodents than wax-free rodenticidal baits. Decrease in attractiveness to the rodents is especially problematic with rodenticides requiring multiple feedings by a rodent. Attractiveness must be maintained for the rodent to return to ingest sufficient rodenticide.
It is against this background that the significant improvements and advancements of the present invention have taken place.